Night shift workers may be at a greater risk of developing ovarian cancer, according to a new study. However, the risk may not be as pronounced in women who describe themselves as a 'night person.'

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Thursday, March 14, 2013 — Working the night shift may do more than just mess up your sleep schedule, according to a new study, published in the journal Occupational and Environmental Medicine. Researchers from the Fred Hutchinson Cancer Research Center in Seattle found that women working the night shift may be at a higher risk for ovarian cancer — but results show that the degree of risk may be lower in women who think of themselves as night people.

The researchers looked at a total of 3,322 women, 1,101 of whom had the most common form of advanced ovarian cancer and 389 of whom had borderline ovarian cancer. The other women were part of a healthy comparison group. A quarter to a third of the women in the different groups studied reported having worked nights at some point in their lives, on average for 2.7 and 3.5 years apiece.

NIght shift work was associated with a 24 percent higher risk of advanced ovarian cancer and a 49 percent higher risk of early-stage ovarian cancer, the researchers found. However, the risk of cancer was 7 percent lower in women who described themselves as night types.

“We found evidence suggesting an association between shift work and ovarian cancer,” the researchers, led by Dr. Parveen Bhatti, an epidemiology researcher at the Fred Hutchinson Cancer Research Center, wrote in the study. “However, there was suggestive evidence of a decreased risk of ovarian cancer among women reporting a preference for activity during evenings rather than mornings.”

Approximately 22,000 women are diagnosed with ovarian cancer every year in the United States, according to the study, and over 15,000 of them will die from the disease. There are very few known risk factors, the researchers wrote in the study, which makes further research to better understand how shift work raises your risk crucial.

“Given the high mortality rate among patients with ovarian cancer,” the researchers wrote in the study, “the identi?cation of potentially modi?able risk factors is crucial to disease prevention efforts.”

But Gloria Huang, MD., associate professor of obstetrics and gynecology at the Albert Einstein College of Medicine and attending gynecologist-oncologist at Montefiore Medical Center, said it may be more than just low melatonin levels that put shift workers at an increased risk of ovarian cancer.

“The relation between shift work and cancer may not be simply due to melatonin suppression,” she said, “but could be mediated by other effects of sleep deprivation.”

Shift work has also been linked to a variety of other diseases, including diabetes, multiple sclerosis and breast cancer, which Huang said could all be linked to the poor sleep habits of shift workers. She said it’s imperative that people on the night shift do everything they can to get enough sleep to help ward off the various conditions associated with their type of work.

“Having a darkened room when you do sleep can improve the quality of sleep, and would help restore melatonin levels,” she said. “It’s important that when you do sleep, you do everything you can to improve the quality of it.”

The researchers said they couldn’t explain why self-described night types were at a lower risk for ovarian cancer, but in an editorial accompanying the study, Thomas Erren, a researcher at the Institute and Polyclinic for Occupational Medicine in Germany, said the findings may force a change in the definition of what shift work actually is.

“Ultimately, we may want to define shift work specifically for an individual as ‘work at chronobiologically unusual times’, he said, “that is, the time window of the work is not readily compatible or ‘in phase’ with the individual’s ‘time-of-day-type.’”

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